Iron is a vital nutrient for the vast majority of organisms. Gram-positive bacteria, Gram-negative bacteria and archaea established different strategies to utilize iron from various sources. This article concentrates on the cytoplasmic membrane-associated uptake systems involved in the acquisition of iron. Genetic, biochemical and structural data as well as computational analyses were taken into consideration. Besides divalent metal transporters of the Nramp type and ferrous iron transport proteins of the Feo type, four distinct families of ABC transporters related to iron uptake are known. Their components mediate the transfer of iron, siderophores, heme and vitamin B₁₂ into the cytosol of prokaryotes.